DISSERTATION RESEARCH: Gliding Aerodynamics and the Origin of Bat Flight

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Gliding aerodynamics and the Origin of Bat FlightBy Sharon M. Swartz and Kristin BishopThe question of how a structure that is well adapted for one function evolves into a new structure adapted for a different function without a functional intermediate phase continues to challenge evolutionary biologists. One example of this kind of transition is the evolution of flight in bats from a gliding ancestor. One assumption is that short, broad wings of living mammalian gliders cannot generate enough lift if they are used in flapping flight. Conversely, few bats glide routinely, a second assumption, therefore, is that long, slender bat wings do not work well for gliding. Aerodynamic theory has focused on human-engineered aircraft, so very little is known about small, flexible, slow moving wings such as those of mammalian gliders and bats. To better understand the evolution of flight in bats, the effect of wing shape on the aerodynamics of small, flexible wings will be tested in the present study by building physical models of wings that span a continuum from glider-like to bat-like. The lift and drag forces that are generated at biologically realistic wind speeds will be measured in a wind tunnel. To determine the origin of flight in bats, it is also important to understand the mechanisms of gliding in living mammals. Gliding evolved independently in six separate groups of living mammals that all share similar body shapes and behaviors. This strongly suggests that any gliding ancestor of bats also shared these features, and that the study of gliding mammals can give important insights into bat ancestors. Three-dimensional motion analysis of gliding in three groups of gliding mammals will be used to learn more about gliding behavior in mammals. This information, combined with the physical model data, will allow assessment of the importance of wing shape in a relevant biological context.